Tires may be formed by supplying a material in a flowable form into a mold and after the material hardens, removing the molded tire from the mold. However, it may be desirable for molded tires to have a tread portion that exhibits different material characteristics than other portions of the tire. For example, it may be desirable for the tread portion to have particular friction and wear characteristics that are different than other parts of the tire, such as the portion of the tire between the tread portion and the hub.
For example, in tires for machines it may be desirable to provide tires having a relatively stiff material able to support high loads associated with the weight of the machine and any payload. In contrast, it may be desirable for the tread portion of such a tire to be formed from a material that provides a desired level of traction and resistance to wear. However, it may be difficult to mold a tire formed from a single material that results in this combination of desirable characteristics. Attempts have been made to mold a polyurethane tread material onto a rubber tire. However, the polyurethane tread material may tend to separate from the rubber tire under certain operating conditions due, for example, to high speed, high loads, or high temperatures. As a result, it may be desirable to provide a molded tire that provides a combination of desirable stiffness, traction, and wear resistance.
An example of a method of preparing a composite of polyurethane bonded to the surface of a cured rubber substrate and the resulting composite cushioned tire is disclosed in U.S. Pat. No. 4,669,517 to Krishnan (“the '517 patent”). In particular, the method of the '517 patent requires that the rubber substrate contain an hydroxyl terminated polybutadiene polyol. The method includes first applying to a cleaned, cured rubber surface containing the polybutadiene polyol a coating of cyanuric acid followed by an additional coating of a phenol formaldehyde resin, and then applying a liquid polyurethane reaction mixture, which is cured to form the resultant composite. The method of the '517 patent is particularly directed to the preparation of a tire including a polyurethane carcass applied to a cured rubber tread, and to a tire including a polyurethane tread applied to a cured rubber carcass.
Although the method disclosed in the '517 patent purports to result in a tire including a polyurethane tread applied to a cured rubber carcass, the '517 patent does not disclose a tire or associated method that results in a molded tire having a polyurethane tread portion and a polyurethane support structure, wherein the characteristics of the polyurethane of the tread portion are different than the characteristics of the polyurethane support structure. In addition, the method of the '517 patent may be overly complex and impractical for the large scale production of molded tires.
The molded tire and associated methods disclosed herein may be directed to mitigating or overcoming one or more of the possible drawbacks set forth above.